arXiv:astro-ph/0110583v1 27 Oct 2001 [email protected] l.Ms fteemsigsasaerdMdaf,with dwarfs, sam- M pc red 10 are approx- the missing that from these B missing estimate of Most are (1997) and ple. systems al. 5 a 130 ¿From et within ). imately densities Henry 2001 , al. observed et 10 the Scholz of 2001; al. comparison et Delfosse 1997; ot fdeclination of south vnvr ls oteSn silsrtdb h recent the by illustrated d with as stars , new three the of to discoveries close very even kinematics, statistics. its multiplicity functions, and composition, chemical and of luminosity studies stellar through components, into its Galaxy’s insight our deep of provides nature the also so- sample The neighbourhood mea- effort. significant lar be with can spec- although parallaxes accurately, their trigonometric sured of their examples and the rests studied type, are tral best astronomy they hence objects stellar and individual As brightest of stars. nearest understanding the upon our of Much Introduction 1. edopitrqet to requests offprint Send wl eisre yhn later) hand by inserted be (will Astrophysics & Astronomy − .Phan-Bao N. V ehp upiigy hssml ssilincomplete, still is sample this surprisingly, Perhaps > 1 2 3 4 5 7 6 8 ahn rmpae pnig1 o4 er,adaelre th larger are and , 48 to 13 proper spanning Their anoth plates counterpart. and from DENIS database, machine a DENIS with the cross-identified from and selected directly were 26 Abstract. Accepted / Received e words. Key co DENIS pc. the 30 from and estimated 15 were between distances Their giants. are .0(leee l 96,adtedfii slargest is deficit the and 1986), al. et (Gliese 1.70 etedAayedsIae,DSA,Osraor eParis de Observatoire DASGAL, Images, des d’Analyse Centre bevtied ai DSA/M-63,704Prs Fra Paris, 75014 (DASGAL/UMR-8633), Paris de Observatoire aoaor ’srpyiu eGeol,UiesteJ F Universit´e J. Grenoble, de d’Astrophysique Laboratoire aaaFac-aaiTlsoeCroain 513 Mam 65-1238 Corporation, Telescope Canada-France-Hawaii ntttdAtohsqed ai,9bsbueadArago, boulevard 98bis Paris, de d’Astrophysique Institut EP,Osraor ePrs lc .Jnsn 29 Meud 92195 Janssen, J. France place 4, 5 Cedex Paris, Nice de 06304 Observatoire 4229, DESPA, BP Nice, de Observatoire uoenSuhr bevtr,Csla101 atao19 Santiago 19001, Casilla Observatory, Southern European epeet3 e ery(d nearby new 30 present We e egbus V 0DNSlt- dwarfs late-M DENIS 30 IV. neighbours: New 1 srmty-poe oin o asstars mass low - motions proper - , 2 .Guibert J. , − 30 ◦ . aucitno. manuscript .Pa-a,e-mail: Phan-Bao, N. : 1 , ewe 5ad3 parsecs 30 and 15 between 2 .Crifo F. , < c(er tal. et (Henry pc 6 .Fouqu´eP. < 2 0p)rddafcniae,wt siae pcrltpsM types spectral estimated with candidates, dwarf red pc) 30 .Delfosse X. , 7 , 8 n .Simon G. and , antd ftepoe oinctlge ot fdec- of limiting south brighter catalogues One much motion 2001). lination the proper al. the is et of Jahreiß efforts magnitude 1997; these Reid to (Henry & them limitation Gizis identify 1997; to exam- al. working extreme et are an for groups 2001, Several al. ple). et unrecognized Scholz many (e.g. stars contain nearby therefore the catalogues smaller and the followed-up, Luyten even incompletely resulting date been To the has end. catalogue of faint LHS bias the for motion 1971, least proper at al. a sample, et to (Giclas leads catalogues This Lowell 1978). the the 1979; or LHS 1930), as 1980) 1961; 1918, NLTT 1957, such LTT al. 1955; catalogues, (LFT et motion catalogues last (Porter Luyten proper the catalogues from Cincinnati least targets part the their at good selected a for have for programs However, parallax 1991). Gliese pho- years, 1956; fifty of 1979, (Gliese basis Jahreiß distances the & on spectroscopic included or still tometric avail- some is though the fraction parallaxes, within significant trigonometric selected of catalogues been able have neighbourhood lar odsasi urnl missing. neighbour- currently solar is the of stars fraction hood larger much a where sion), 3 .Forveille T. , uir ..5,F301Geol,France Grenoble, F-38041 53, B.P. ourier, 51 Paris 75014 o h otpr h nw ebr fteso- the of members known the part most the For Chile , or n Rclu-antd eain n range and relations colour-magnitude IR and lours oin eemaue nteMM measuring MAMA the on measured were motions lhaHgwy aul,H 64 USA 96743 HI Kamuela, Highway, alahoa r4wr rtetatdfo h H catalogue LHS the from extracted first were 4 er 1aeu elOsraor,704Prs France Paris, 75014 l’Observatoire, de avenue 61 , n0.1 an nce nCdx France Cedex, on − 33 ′′ ◦ yr 2 eg coze l 01 o eetdiscus- recent a for 2001, al. et Scholz (e.g. − 3 1 , uigottepsiiiyta they that possibility the out ruling , 4 .Borsenberger J. , 5 .Epchtein N. , oM8. to 6 6 , 2 N.Phan-Bao et al.: New neighbours: IV. 30 DENIS late-M dwarfs

I−J Spectral type MI Dlim 2.0 M5.5 - M6 11.5 250 pc 2.5 M6.5 - M7 12.9 130 pc 3.0 M8 14.0 80 pc

Table 1. Typical detection limiting distances (Dlim) for M dwarfs with colour 2.0 ≤ I−J ≤ 3.0 in the DENIS sur- vey. The spectral types are from Leggett (1992) and the is taken from Figure 1.

The recent near-infrared sky surveys, DENIS and 2MASS, represent a powerful alternative tool to identify these faint and cool nearby stars. Candidates are first se- lected on simple colour and photometric distance crite- ria, producing an initial list that also contains many gi- ants, and potentially some pre-main-sequence stars. At Fig. 1. MI : I − J HR diagram for M dwarfs with known low galactic latitudes it would also include many red- distances (from Leggett 1992 and Tinney et al. 1995). Our dened distant stars. In a second step these contaminat- empirical polynomial fit and the 3 Gyr model of Baraffe ing populations need to be rejected, through either (1) et al. (1998) for a solar metalicity are overlaid. a systematic spectroscopic follow up (Gizis et al. 2000), or (2) selection (distant giants have very small proper motions), or (3) more accurate multi-colour (J and Ks) and one optical band (I). DENIS observa- photometry than available from the surveys. Systematic tions are carried out on the ESO 1m telescope at La Silla. Dichroic beam splitters separate the three channels, and spectroscopy is clearly the cleanest approach, and does not ′′ reject the few nearby star that, like Gl 710 for instance, a focal reducing optics provide scales of 3 per pixel on the 256×256 NICMOS3 arrays used for the two infrared have small proper motions. Proper motion selection on ′′ the other hand is cheap and effective, but it obviously channels, and 1 per pixel on the 1024×1024 Tektronix does nothing to correct for the proper motion bias of the CCD detector of the I channel. present nearby star catalogues. The image data were processed with the stan- We are using here the DENIS near infrared sky survey dard DENIS software pipeline (Borsenberger 1997, to identify possible very-low-mass stars within 30 parsecs. Borsenberger et al., in preparation) at the Paris Data We conservatively adopt a distance cutoff slightly larger Analysis Center (PDAC). The thermal background pro- than the 25 pc limit of the Catalogue of Nearby Stars duced by the instrument and the sky emission is de- of Gliese and Jahreiß (CNS3, 1991), to avoid losing bona- rived from a local clipped mean along the strip. Flat- fide d < 25 pc stars from imprecise photometric distances. field corrections are derived from observation of the sun- One initial result of this effort was the discovery of an M9 rise sky. Source extraction and photometry are performed dwarf at a spectroscopic distance of only 4 pc, DENIS- at PDAC, using a space-varying kernel algorithm (Alard P J104814.7-395606.1 (Delfosse et al. 2001). In this paper 2000). The astrometry of the individual DENIS frames is ′′ we present 26 nearby red dwarf candidates, selected with referenced to the USNO-A2.0 catalogue, whose ∼ 1 ac- I−J > 2.0 (M6 or later) in the DENIS database and with curacy therefore determines the absolute precision of the a proper motion larger than 0.1′′yr−1. 13 of these are new, DENIS positions. and another 13 were known as high-PM objects but had With a 100% completeness level at I∼18.0, J∼16.0 and not been characterized further. Four additional candidates Ks ∼13.0, the DENIS survey is sensitive to M dwarfs out were first selected from the southern part of the LHS cat- to large distances (Table 1), well beyond the 25 pc limit alogue and then identified with DENIS counterparts. of the CNS3 (1991). In this part of the HR diagram the Sect. 2 reviews the sample selection, and Sect. 3 I−J (or alternately I−K) colour index is an excellent spec- presents the photographic photometry and the proper mo- tral type and luminosity estimator (Leggett 1992). The tion measurements. We discuss the results in Sect. 4 and DENIS data therefore provide immediate identification of summarize in Sect. 5. M dwarf candidates from I−J > 1.0, and, under the as- sumption that they are indeed dwarfs, a good estimate of their distance through colour-magnitude relations. Color- 2. Sample selection magnitude relations have yet to be established for the na- 2.1. DENIS observations tive DENIS photometric system, and we therefore resort to a relation in the standard Cousins-CIT system to de- The DEep Near-Infrared Survey (DENIS) is a southern rive distances for red stars in the DENIS database. A pre- sky survey (Epchtein 1997), which will provide full cover- liminary comparison of the two photometric systems for age of the southern hemisphere in two near-infrared bands very late M dwarfs shows differences of ∼0.1 mag between N.Phan-Bao et al.: New neighbours: IV. 30 DENIS late-M dwarfs 3

Table 2. Position and observation information for the 30 new nearby star candidates

DENISName Othername α2000 δ2000 DENIS Number of Time observations baseline [yr] DENIS-P J0004575−170937 ... 00 04 57.54 −17 09 37.0 1999.521 4 47.834 DENIS-P J0013466−045736 LHS 1042 00 13 46.60 −04 57 36.5 1999.846 4 45.173 DENIS-P J0019275−362015 ... 00 19 27.53 −36 20 15.7 1999.877 3 21.064 DENIS-P J0041353−562112 ... 00 41 35.39 −56 21 12.9 1999.803 3 20.984 DENIS-P J0145434−372959 ... 01 45 43.49 −37 29 59.3 1999.877 3 22.165 DENIS-P J0253444−795913 ... 02 53 44.41 −79 59 13.6 1999.699 3 21.921 DENIS-P J0312251+002158 ... 03 12 25.11 +00 21 58.6 1999.704 3 48.020 DENIS-P J0324268−772705 ... 03 24 26.88 −77 27 05.5 1999.855 3 22.077 DENIS-P J0413398−270428 LP 890- 2 04 13 39.81 −27 04 28.9 1999.838 4 41.869 DENIS-P J0602542−091503+ LHS 1810 06 02 54.26 −09 15 03.8 1999.929 3 17.040 DENIS-P J0848189−201911+ LHS 2049 08 48 18.94 −20 19 11.4 1999.258 3 21.014 DENIS-P J1003191−010507+ LHS 5165 10 03 19.18 −01 05 07.7 1999.030 3 13.011 DENIS-P J1136409−075511 LP 673-63 11 36 40.99 −07 55 11.7 1999.373 4 45.195 DENIS-P J1216101−112609 LP 734-87 12 16 10.16 −11 26 09.9 1999.203 4 44.948 DENIS-P J1223562−275746 LHS 325a 12 23 56.27 −27 57 46.7 1999.304 4 41.162 DENIS-P J1236153−310646 LP 909-55 12 36 15.32 −31 06 46.0 1999.249 4 41.923 DENIS-P J1357149−143852 ... 13 57 14.97 −14 38 52.6 1999.225 4 44.959 DENIS-P J1406493−301828+ LHS 2859 14 06 49.33 −30 18 28.0 1999.395 3 24.927 DENIS-P J1412069−041348 LP 679-32 14 12 06.98 −04 13 48.2 1999.444 4 42.118 DENIS-P J1553251−044741 ... 15 53 25.13 −04 47 41.3 1999.581 4 45.170 DENIS-P J1614252−025100 LP 624-54 16 14 25.20 −02 51 00.5 1999.280 4 45.763 DENIS-P J2002134−542555 ... 20 02 13.42 −54 25 55.7 1999.581 4 23.077 DENIS-P J2049527−171608 LP 816-10 20 49 52.72 −17 16 08.6 1999.518 3 44.946 DENIS-P J2107247−335733 ... 21 07 24.73 −33 57 33.3 1999.581 4 19.812 DENIS-P J2134222−431610 WT 792 21 34 22.27 −43 16 10.4 1999.767 3 21.189 DENIS-P J2202112−110945* LP 759-17 22 02 11.28 −11 09 45.8 1999.419 4 45.672 DENIS-P J2213504−634210 WT 887 22 13 50.47 −63 42 10.0 1999.537 3 22.976 DENIS-P J2331217−274949 ... 23 31 21.73 −27 49 49.9 1999.869 5 45.119 DENIS-P J2333405−213353 LHS 3970 23 33 40.59 −21 33 53.2 1999.770 4 45.176 DENIS-P J2353594−083331 ... 23 53 59.44 −08 33 31.6 1999.693 3 46.077

+ Objects selected from LHS initially ∗ Already listed by Gizis et al. (2000) Columns 1 & 2: Object name in the DENIS data base and other identification if available. Columns 3, 4 & 5: DENIS Position with respect to equinox J2000 at DENIS epoch. Columns 6 & 7: Number of position observations and time baseline. the K bands, of slightly less than 0.05 mag between the lation, J bands, and below 0.05 mag between the two I bands 2 3 (Delfosse 1997b). We therefore choose to determine dis- MI = 4.97 − 4.76(I − J)+10.03(I − J) − 4.07(I − J) 4 tances from the (I−J , MI) relation, which is least affected +0.53(I − J) , (1) by the neglected colour terms, and note that systematic errors from adopting the Cousins-CIT relation are much valid for 1.0

Table 3. 34 red DENIS stars with µ< 0.1′′yr−1, not kept for further investigation in the present paper

DENIS Name α2000 δ2000 DENIS I I−J J−K Epoch DENIS-P J0013093−002551 00 13 09.34 −00 25 51.5 1999.838 14.37 2.22 0.88 DENIS-P J0100021−615627 01 00 02.13 −61 56 27.1 1999.964 15.01 2.42 0.94 DENIS-P J0250072−860930 02 50 07.20 −86 09 30.0 1999.712 9.26 2.09 1.41 DENIS-P J0441247−271453 04 41 24.70 −27 14 53.6 1999.063 8.92 2.19 1.20 DENIS-P J1117420−264453 11 17 42.08 −26 44 53.8 1999.266 11.71 2.16 0.56 DENIS-P J1236396−172216 12 36 39.61 −17 22 16.9 1999.384 13.91 2.14 1.14 DENIS-P J1400335−271656 14 00 33.51 −27 16 56.2 1999.348 9.69 2.09 1.26 DENIS-P J1405376−221515 14 05 37.64 −22 15 15.0 1999.285 9.49 2.09 1.29 DENIS-P J1427297−264040 14 27 29.71 −26 40 40.8 1999.419 9.68 2.12 1.20 DENIS-P J1510397−212524 15 10 39.72 −21 25 24.9 1999.384 10.06 2.22 1.18 DENIS-P J1525014−032359 15 25 01.46 −03 23 59.5 1999.351 9.25 2.09 1.08 DENIS-P J1552237−033520 15 52 23.78 −03 35 20.7 1999.534 12.02 2.07 1.37 DENIS-P J1552551−045215 15 52 55.19 −04 52 15.3 1999.534 10.21 2.01 1.38 DENIS-P J1553186−025919 15 53 18.65 −02 59 19.3 1999.581 13.12 2.04 1.36 DENIS-P J1615446−040526 16 15 44.69 −04 05 26.2 1999.353 9.67 2.03 1.19 DENIS-P J1618120−044221 16 18 12.09 −04 42 21.8 1999.386 11.32 2.26 1.28 DENIS-P J2024329−294402 20 24 32.96 −29 44 02.6 1999.392 10.45 2.13 1.26 DENIS-P J2032270−273058 20 32 27.03 −27 30 58.4 1999.534 10.76 2.45 1.18 DENIS-P J2034203−263652 20 34 20.33 −26 36 52.2 1999.712 11.27 2.23 1.12 DENIS-P J2044066−173457 20 44 06.68 −17 34 57.3 1999.606 11.28 2.42 1.29 DENIS-P J2055240−322600 20 55 24.07 −32 26 00.8 1999.669 10.73 2.10 1.30 DENIS-P J2056329−782540 20 56 32.90 −78 25 40.1 1999.660 10.43 2.08 1.20 DENIS-P J2058075−730350 20 58 07.55 −73 03 50.4 1999.660 11.89 2.35 1.29 DENIS-P J2103375−783831 21 03 37.56 −78 38 31.5 1999.658 11.42 2.08 1.30 DENIS-P J2124575−341655 21 24 57.51 −34 16 55.9 1999.559 13.60 2.37 1.32 DENIS-P J2125399−100526 21 25 39.98 −10 05 26.1 1999.482 12.25 2.10 0.59 DENIS-P J2130021−815158 21 30 02.15 −81 51 58.6 1999.510 10.33 2.17 1.37 DENIS-P J2155040−165535 21 55 04.06 −16 55 35.1 1999.712 12.46 2.37 0.40 DENIS-P J2203522−593300 22 03 52.29 −59 33 00.7 1999.649 11.29 2.43 1.16 DENIS-P J2206227−204706 22 06 22.78 −20 47 06.0 1999.611 15.09 2.67 1.22 DENIS-P J2225004−121606 22 25 00.48 −12 16 06.9 1999.447 10.38 2.25 1.19 DENIS-P J2226443−750342 22 26 44.36 −75 03 42.7 1999.814 15.20 2.84 1.20 DENIS-P J2312219−091513 23 12 21.98 −09 15 13.5 1999.482 13.70 2.99 0.29 DENIS-P J2334544−193232 23 34 54.49 −19 32 32.4 1999.707 14.63 2.94 0.54

Columns 1: Object name. Columns 2, 3 & 4: DENIS Position with respect to equinox J2000 at DENIS epoch. Columns 5, 6 & 7: DENIS I-magnitude and colours. polynomial colour-magnitude relations, and retain those quences are distinct in the DENIS I−J/J−K colour-colour with Dphot ≤ 30 pc. In the present paper we focus on diagram, but not sufficiently separated to distinguish the the 2.0 < I−J < 3.0 range, or spectral types of approx- two classes with 100% completeness and reliability. imately M6 to M8. Bluer nearby M dwarfs are brighter and hence less likely to have been overlooked. At present we therefore give them a lower priority. Redder ones, like 2.2. Additional candidates from the LHS catalogue DENIS-P J104814.7-395606.1 (Delfosse et al. 2001), are addressed by the DENIS Brown Dwarf program (Delfosse We additionally browsed the LHS catalogue (Luyten 1979) et al., in preparation). for objects that match the colour and photometric dis- tance criteria, but which had been missed because of our These criteria are met by 60 objects (Table 2, 3), 13 galactic latitude cutoff, or whose DENIS observations had of which are listed in proper motion catalogues but had not yet been entered in the database. To narrow down no distance estimate (except WT 792, discussed below). that search, we looked for unambiguous DENIS identifi- At that stage the sample is a mix of distant giants and cations to southern LHS stars matching BLuyten > 16.0, nearby dwarfs, which cannot be completely separated us- RLuyten > 15.0, and BLuyten−RLuyten > 1.5, and then ap- ing the DENIS photometry alone: the dwarf and giant se- plied the colour and photometric distance cutoffs. This N.Phan-Bao et al.: New neighbours: IV. 30 DENIS late-M dwarfs 5

Table 4. Proper motion of the 30 Nearby Star candidates

DENIS Name µα µδ µtotal µL/W ′′ − ′′ − ′′ − ′′ − [ yr 1] [ yr 1] [ yr 1] [ yr 1] J0004575−170937* +0.146 −0.011 0.146 ... J0013466−045736 +0.584 −0.153 0.604 0.619 J0019275−362015* +0.152 −0.097 0.180 ... J0041353−562112* +0.121 −0.064 0.137 ... J0145434−372959* +0.424 −0.118 0.440 ... J0253444−795913* +0.074 +0.081 0.110 ... J0312251+002158* +0.173 −0.028 0.176 ... J0324268−772705* +0.287 +0.184 0.341 ... J0413398−270428 +0.234 −0.023 0.235 0.230 J0602542−091503 +0.172 −0.616 0.639 0.608 J0848189−201911 +0.342 −0.593 0.685 0.633 J1003191−010507 −0.497 +0.056 0.500 0.491 Fig. 2. All DENIS sources with the I−J colour of an M- J1136409−075511 −0.171 +0.144 0.224 0.223 dwarf (1.0 < I−J < 3.0) detected in the first 2110 squares − − J1216101 112609 +0.041 0.219 0.223 0.212 degrees processed by PDAC, with a photometric distance − − J1223562 275746 1.239 +0.323 1.280 1.293 ≤ 30 pc and a galactic latitude ≥ 30◦. The dots repre- J1236153−310646 +0.161 −0.083 0.181 0.191 sent the early M-stars (1.0 < I−J < 3.0). Amongst the J1357149−143852* −0.355 +0.023 0.356 ... J1406493−301828 −0.855 −0.059 0.857 0.814 60 DENIS sources in the 2.0−3.0 range (corresponding J1412069−041348 +0.292 −0.152 0.329 0.342 to a late-M spectral class) the solid circles represent the ′′ −1 J1553251−044741* −0.034 −0.121 0.126 ... objects with a proper motion µ > 0.1 yr , and the tri- J1614252−025100 +0.003 +0.367 0.367 0.401 angles those with a smaller proper motion. The solid and J2002134−542555* +0.060 −0.364 0.369 ... dashed lines respectively represent the dwarf and giant J2049527−171608 +0.303 −0.102 0.320 0.305 sequences of Bessell & Brett (1988), for slightly different J2107247−335733* +0.344 −0.367 0.503 ... filters. The (indicative) spectral type labels on the top axis J2134222−431610 +0.142 −0.792 0.804 0.785 are adopted from Leggett 1992. J2202112−110945 +0.137 −0.182 0.228 0.210 J2213504−634210 +0.140 +0.166 0.217 0.195 J2331217−274949* +0.087 +0.738 0.744 ... − − CNS3 and the Hipparcos catalogue that have a proper J2333405 213353 +0.682 0.336 0.761 0.794 ′′ −1 J2353594−083331* −0.039 −0.367 0.369 ... motion smaller than 0.1 yr . In the CNS3, this fraction of ”slow” stars is about 13% for limiting magnitudes of ∗ Not previously known as a high proper motion star V < 7, 8 and 9. In the Hipparcos catalogue and for the Columns 2, 3 & 4: µα, µδ, µtotal our measurement, in arc- same limiting magnitudes it is much lower, only 6.5%. The − sec.yr 1. CNS3 is considered complete to V = 9. The Hipparcos cat- Columns 5: Literature total proper motion, from Luyten alogue is complete up to V = 7.3, and nearly complete up (1979, 1980) or Wroblewski et al. (1994) when available. to at least 9 for nearby stars, as potential nearby stars were systematically included in the Hipparcos Input cat- alogue. Incompleteness therefore cannot explain the dis- identified 4 additional candidates: LHS 1810, 2049, 2859 crepancy between the fractions of low proper-motion stars and 5165, which are added in the Tables. in the two catalogues. A careful comparison between the two lists of ”slow” stars shows that half of the slow CNS3 objects have a Hipparcos distance larger than 25 pc, and 3. Proper motions and B, R photometry should therefore not be taken into consideration. The frac- As an initial step towards rejecting giants, we determine tion of nearby stars lost due to our proper motion cut-off is the proper motion of the candidates from a comparison therefore of the order of 6%. Our future goal is to obtain of the DENIS position with archival Schmidt plates dig- spectra of all candidates, independently of their proper itized on the MAMA microdensitometer. Objects fainter motions, to assemble a complete and unbiased inventory than R = 10 with a proper motion µ ≥ 0.1′′yr−1 must of the solar neighbourhood for the high galactic latitude be dwarfs: a red giant with such an southern sky. and proper motion would have a very large and improb- To obtain B and R photometry of the candidates and able space velocity (≥ 1000 km/s), much larger than the determine their proper motions, we identified all Survey Galactic escape speed (Meillon 1999). Conversely, some plates in the CAI (http://dsmama.obspm.fr/) plate vault small fraction of the nearby dwarfs must have proper mo- that contained images of the nearby star candidates. tions below our cutoff. To estimate that proportion, we Depending on the of the candidates, the fol- counted the fraction of the stars within 25 pc in both the lowing plates were available: POSS I for −30◦ <δ< 0◦,

6 N.Phan-Bao et al.: New neighbours: IV. 30 DENIS late-M dwarfs 1

Fig. 3. I-band finding charts for the objects listed in Table 2. The size of each chart is ∼ 3.5′ × 3.5′. North is up and east is to the left. The 4 stars selected directly from the LHS are not included. N.Phan-Bao et al.: New neighbours: IV. 30 DENIS late-M dwarfs 7

Table 5. MAMA and DENIS photometry, and estimated distances, for the 30 DENIS red dwarf candidates

DENISobjects B R I I−J J−K MI MK DistI DistK Vt [pc] [pc] [km/s] J0004575−170937 18.2 15.6 13.00 2.03 0.93 11.59 8.78 19.1 17.8 13.2 J0013466−045736 19.5 16.8 13.88 2.44 0.99 12.73 9.69 17.0 14.2 48.7 J0019275−362015 18.2 17.0 14.30 2.14 0.89 11.95 8.95 29.6 29.1 25.3 J0041353−562112 20.6 18.7 14.68 2.74 1.07 13.37 10.12 18.2 14.1 11.8 J0145434−372959 20.2 17.7 15.05 2.56 0.94 13.00 9.79 25.7 22.5 53.6 J0253444−795913 18.7 16.2 13.47 2.15 0.98 11.98 9.17 19.9 17.1 10.4 J0312251+002158 20.4 17.0 14.30 2.17 0.93 12.03 9.11 28.4 26.2 23.7 J0324268−772705 20.4 17.3 14.36 2.26 1.04 12.29 9.49 26.0 20.6 42.0 J0413398−270428 22.0 17.7 14.45 2.26 0.99 12.29 9.40 27.1 22.9 30.2 J0602542−091503 17.3 15.6 12.98 2.12 0.85 11.88 8.81 16.6 17.4 48.9 J0848189−201911 19.7 17.2 14.51 2.21 0.98 12.15 9.29 29.7 25.4 88.3 J1003191−010507 21.0 18.0 14.94 2.62 1.08 13.12 10.02 23.1 17.6 51.7 J1136409−075511 17.8 16.5 14.31 2.20 0.90 12.12 9.11 27.4 26.3 29.1 J1216101−112609 19.5 17.1 14.72 2.30 1.10 12.39 9.65 29.2 21.6 30.9 J1223562−275746 19.6 16.4 14.19 2.30 0.88 12.39 9.27 22.9 22.3 138.9 J1236153−310646 18.5 16.7 13.97 2.23 1.01 12.21 9.39 22.5 18.6 19.3 J1357149−143852 21.1 18.5 15.55 2.69 1.14 13.27 10.13 28.5 20.8 48.1 J1406493−301828 18.5 15.7 13.42 2.13 1.01 11.91 9.19 20.0 16.5 77.5 J1412069−041348 19.1 16.3 13.66 2.04 0.98 11.63 8.93 25.5 22.0 39.8 J1553251−044741 17.4 15.1 13.67 2.10 1.37 11.82 9.75 23.4 12.3 14.0 J1614252−025100 19.3 17.3 13.63 2.29 1.04 12.37 9.54 17.9 14.2 31.1 J2002134−542555 19.4 17.1 13.89 2.20 1.18 12.12 9.62 22.6 15.1 39.5 J2049527−171608 18.9 16.8 14.16 2.32 1.08 12.44 9.65 22.0 16.7 33.4 J2107247−335733 19.9 16.7 14.36 2.20 1.02 12.12 9.35 28.0 22.8 66.8 J2134222−431610 17.6 15.3 12.78 2.02 1.06 11.56 9.07 17.5 13.4 66.7 J2202112−110945 20.7 17.9 15.11 2.66 0.98 13.21 9.96 24.0 20.1 25.9 J2213504−634210 18.7 16.3 13.05 2.16 1.04 12.01 9.31 16.2 12.8 16.7 J2331217−274949 20.4 17.7 14.25 2.59 1.04 13.06 9.94 17.3 13.6 61.0 J2333405−213353 19.3 16.5 13.89 2.06 0.90 11.69 8.78 27.5 26.9 98.2 J2353594−083331 ** 18.6 15.93 2.97 1.13 13.92 10.32 25.3 20.0 44.3

∗∗ Too faint for the plate Column 1: Object name. Columns 2, 3: B, R magnitudes determined from the plates using GSPC and GSPC-2 calibrations. Columns 4, 5, 6: DENIS I-magnitude and colours. Column 7: MI absolute I band magnitude, from the colour magnitude relation derived in the present paper. Column 8: MK absolute K band magnitude, from the Tinney et al. (1995) relation. Columns 9, 10: DistI, DistK distances estimated from MI and MK respectively. Column 11: Vt tangential velocity, computed from DistI and the proper motion.

SRC-J for −90◦ <δ< 0◦, SRC-R for −17◦ <δ< 0◦, and the full sample of 60 objects, 34 have no proper motion ESO-R for δ < −17◦. We used the MAMA microdensit- above the 0.1′′yr−1 level and are listed in Table 3. They ometer (Berger et al. 1991) at CAI to digitize the survey are not studied in this paper, and leave us with 26 high plates, and analysed the resulting images with SExtractor quality nearby star candidates (Table 2) to which the 4 (Bertin & Arnouts 1996). The SExtractor source param- LHS stars are added (finding charts in Fig. 3). Of the 30 eters were calibrated using the GSPC-2 (Postman et al. proper-motion objects, 13 were previously unknown. 2 of 1997, Bucciarelli et al. 2001) and ACT catalogues (Urban those have a proper motion, µ > 0.5′′yr−1, that would et al. 1998) as photometric and astrometric references to have qualified them for inclusion in the LHS. An addi- produce B and R magnitudes (Table 5), and equatorial tional 5 have µ> 0.2′′yr−1 and could have been included coordinates at the epoch of the plate. Absolute proper in the NLTT. The 17 remaining objects belong to the LHS, motions were then determined through a least square fit the NLTT, or the Catalogue of New proper motion stars to the positions at the 2 to 4 Schmidt plate epochs and (Wroblewski & Torres 1994). For those, the difference be- the DENIS survey epoch. The proper motion errors range tween our proper motions and the literature values has a between 8 and 19 mas/, depending on the object mag- mean of 9 masyr−1 and a dispersion of 23 masyr−1, of nitude and the available time baseline. The magnitude the order of the quoted LHS accuracy. Table 4 lists our errors are ±0.3 mag for B and ±0.2 mag for R. ¿From proper motion measurements, and the literature proper 8 N.Phan-Bao et al.: New neighbours: IV. 30 DENIS late-M dwarfs motion when available. Figure 2, which distinguishes the The 2110 square degrees explored here contain 26 stars high and low proper motion stars in the I−J/J−K di- with 2.0 < I−J < 3.0, µ > 0.1′′yr−1, and a photometric agram, immediately shows that the high proper motion distance d < 30 pc. The whole celestial sphere therefore stars belong to the dwarf sequence, with only one excep- contains ∼ 500 similar objects, of which ∼ 60%, or 300, tion, DENIS-P J1553251-044741.On the other hand, some will have a photometric distance below 25 pc. Malmquist low proper motion stars do, as expected, seem to belong bias from our approximate photometric distances must to the dwarf sequence. bias this number up, and the number of stars that are actually within 25 pc must be significantly smaller, per- haps by as much as a factor of 2. The (R−I)C colour index 4. Discussion that corresponds to our I−J = 2.0 cutoff is (R−I)C = 2.0 (Leggett 1992), or about 1.6 in the Kron system used in In addition to the (I , I−J) distances computed from the the CNS3. The whole CNS3 contains only 23 stars with relation derived above, Table 5 contains (I , I−K) dis- (R−I) > 1.6. An effort similar to ours over the whole tances derived using the (I−K , M ) colour-magnitude Kron K celestial sphere would thus identify 150 to 250 new stars relation of Tinney et al. (1995) for 1.2

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